The present invention relates to a process for the preparation of a lactone from the corresponding cyclic ketone. More particularly, the present invention relates to a process for biotransformation of a cyclic ketone to the corresponding lactone. The process of this invention comprises an efficient, easy and environmentally friendly method for biotransformation of cyclic ketones to corresponding lactones using naturally occurring biomaterials such as fungi.
Lactones are an important class of molecules for the food industry because of their highly aromatic fruity aroma. Lactones, particularly caprolactone and valerolactone, are also used as monomers for preparing biodegradable polymers. Additionally, the oxidation of ketones to esters and lactones by the Baeyerxe2x80x94Villiger reactions is a reliable and highly useful transformation in synthetic chemistry.
The most common and conventional method for preparing lactones from cyclic ketones is based on the use of reagents like peroxycarboxylic acids (e.g. peracetic acid). The main drawback of such chemical methods using per-acids is that they are of hazardous nature and are detrimental to the environment. A catalytic method for the oxidation of ketone to lactones using solid titanium silicate (TS-1) catalyst and dilute hydrogen peroxide (H2O2) has been reported (see A. Bhaumik, P. Kumar and R. Kumar, Catalysis Letters, volume 40, year 1996 and page number 47-50). However, in the case of chemical, catalytic method involving TS-1 and dilute H2O2, the efficiency of utilization of H2O2 is low, rendering the process costly and uneconomic for commercial exploitation.
Enzymatic transformation of cyclohexanone and cyclopentanone to corresponding lactones using enzymes isolated from microorganism Acinetobacter has been reported (see M. J. Taschner and D. J. Black, Journal of American Chemical Society, Vol. 110, year 1988, p. 6892; F. Secundo, G. Carrea, S. Riva, E. Battistel, D. Bianchi, Biotechnology Letters, Vol. 15, 1993, p. 865) and Nocardia globerula C11 (see D. B. Norris and P. W. Trudgil, Biochemical Journal, Vol. 12, 1971, p.3737). Certain strains of Fusarium species are claimed to be active biocatalysts for styrene epoxidation (Japanese patent Jpn. Kokai Tokkyo Koho, No. JP 62236497, 1987).
The main drawback of prior art biological methods using isolated enzymes and co-factors like NADPH is that the isolation of enzyme is cumbersome and time consuming. Further, the use of very costly co-factors makes the process economically unattractive. Another disadvantage of using isolated enzymes and co-factors like NADPH is that the isolation and separation of product from the reaction mixture is tedious.
The main object of the present invention is to provide a new process for the biotransformation of cyclic ketones to lactones obviating the above mentioned drawbacks.
Another object of the present invention is to use the whole fungal mycelial mass as biocatalyst where the separation of the biocatalyst from the product mixture is carried out easily by conventional methods like filtration or centrifugation.
Yet another object of the present invention is to carry out the biotransformation without using any extremely added expensive co-factor like NADPH.
Yet another object of the present invention is to use water as a reaction medium in an environmentally friendly reaction conditions.
Accordingly, the present invention provides a process for the preparation of a lactone from the corresponding cyclic ketone, comprising treating wet fungal mycelia with an alcoholic solution of a cyclic ketone substrate at a temperature in the range of 15 to 40xc2x0 C. for a period ranging between 2 to 200 hours and separating the biomass to obtain the lactone.
In one embodiment of the invention, the cyclic ketone used is selected from C5 to C6 ketones, preferably cyclopentanone and cyclohexanone.
In a further embodiment of the invention, the alcohol used to prepare the alcoholic solution of the cyclic ketone substrate is ethanol.
In another embodiment of the invention, the wet fungal mycelia is obtained by growing the fungus Fusarium oxysporum f. sp. ciceri (NCIM 1282) species in a culture medium for a period of at least 2 hours at a temperature ranging between 15 to 40xc2x0 C. under aseptic conditions, separating the biomass, washing, and then incubating the whole reaction mixture at 15 to 40xc2x0 C. under shaking conditions and atmospheric pressure.
In one embodiment of the invention, the biomass is separated by centrifugation or filtration.
In another embodiment of the invention, the biomass is washed several times with sterile water.
In a further embodiment of the invention, the whole reaction mixture is incubated while shaking at 200 rpm.
In another embodiment of the invention, the culture medium comprises malt extract-glucose-yeast extract -peptone.
In another embodiment of the invention the concentration of the substrate per gram of the wet fungal mycelia is in the range of 1 to 50 mg, preferably 3-30 mg substrate per gram of the wet fungal mycelia and most preferably in the range of 5-10 mg substrate per gram of the wet fungal mycelia.
In yet another embodiment of the invention, the reaction between substrate and wet fungal mycelia is preferably carried out in water with the ratio of wet fungal mycelia to water being in the range of 1 and 100 (w/w).
In yet another embodiment of the invention, the incubation/reaction temperature is in the range of 23-33xc2x0 C., preferably 25-29xc2x0 C.